The objective of this study is to investigate the mechanism(s) underlying differences in dietary fat-induced elevation of plasma high density lipoprotein (HDL) between atherosclerosis resistant cebus monkey (cebus albifrons) and the atherosclerosis-susceptible squirrel monkey (Saimiri sciureus). Our initial attempt will be to fully characterize the HDL in the two species paying special attention to apoprotein and particle size determinations. Particular emphasis will be given to the effect of dietary fat and species susceptibility to atherosclerosis on HDL synthesis and catabolism and how HDL metabolism is associated with HDL composition and particle size. These studies are unique because they not only utilize primate models that differ in their degree of atherosclerosis susceptibility, but permit the investigation of mechanisms regulating HDL levels in primate species whose HDL concentration can be manipulated by dietary means.